This invention relates to a process for etching a silicon substrate using an alkaline solution. More particularly, this invention relates to a silicon etching process that uses a polymeric coating as a mask to limit etching to a selected region. In one aspect, this invention forms a V-groove for a coupling between an optical fiber and an optoelectronic module.
It has been proposed to produce an optoelectronic assembly that comprises a module coupled to an optical fiber for transmitting light signals to or from the module for processing. The module comprises one or more optoelectronic components, such as a light emitting diode or a PIN detector, mounted on a substrate and optically coupled to a waveguide, also carried on the substrate. It has also been proposed to form the substrate of silicon and to provide a V-groove etched in the substrate for receiving an end section of the optical fiber that is aligned with an end of the waveguide for transmitting signals therebetween.
It is known to anisotropically etch a silicon substrate by treatment with an alkaline solution. A mask is applied to the substrate about the region to be etched. A preferred mask material is silicon dioxide that is integrally formed on the substrate by surface oxidation. Processes for forming and etching a silicon dioxide layer require elevated temperatures that tend to damage other features of the module. On the other hand, formation of the groove prior to the other optoelectronic feature complicates spin coating and other steps that are adapted for a planar surface. Thus, it is desired to delay forming the groove to provide a planar surface during early stages of the manufacturing operation, and to subsequently etch the silicon substrate without damage to features already formed.